An initial range-finding study was conducted to establish a dose of World Trade Center dust (WTCD) that resulted in a minimal inflammatory response in the rat lung (measured by BALF analysis). WTCD was administered by intratracheal instillation to male F344 rats. Based upon these results, a time course study was designed to evaluate potential delayed or persistent effects of WTCD. Rats were treated with 0.8 mg/kg of either WTCD, or titanium dioxide (TiO2) particles for three consecutive days. TiO2 particulates were approximately the same size range as the WTCD. The effects of instilling TiO2 in the lung are well characterized and represent the response of the lung to the physical presence of a non-chemically reactive chemical. The TiO2 data will serve as a "benchmark" to compare data from WTCD-treated animals. Pulmonary function, bronchoalveolar lavage fluid indices and histopathology are being evaluated at 4, 8, and 16 weeks after exposure.